1. Field of the Invention
The invention disclosed herein relates to boring and penetrating the earth and, in particular, to a blasthole drilling rig with a magazine for successively moving unconnected oriented shaft sections.
2. Description of the Related Art
Articulated drill pipe positioner mechanisms have been used in the industry of blasthole drilling for some time. Typically such positioners include one or two moveable jaws, which close axially against opposite sides of the drill pipe by the use of a hydraulic force. The combined jaws, when closed, serve to act as a lower anchoring point or bushing, to retain center control of the drill pipe and lessen side loads which would otherwise be transmitted to the rotary head gearbox. The pipe positioner also minimizes pipe bow due to column deflection. Axial and rotational movement of the drill pipe is permitted, as the jaws do not tightly clamp to the pipe. The jaws open and swing out of the way on an articulated arm when drilling operations require the pipe to be changed, and when the rotary head gearbox is at the lower end of its travel within the mast, so as to eliminate interference.
In certain conditions, excessive load may be applied to the drill pipe and pipe positioner by an out-of-sequence operator command, which attempts to move the drill pipe out of the pipe positioner by forcing the pipe to displace in a radial direction. Due to limitations within the operating control system logic, it is not feasible to lock out the possibility of overload without impairing normal drilling operations. This overload may induce mechanical failure of the pipe positioner or its supporting articulated arm, or the structure of the mast. Such damage can be costly to repair, and renders the drilling rig inoperable until repairs can be effected. The purpose of this invention is to provide a means to perform the same intended function as traditional pipe positioner jaws, while acting as a mechanical fuse to prevent damage in the event of an overload condition.
Therefore, what is needed is method and apparatus that provide location control of the drill pipe during operation and secure transport for a lower end of the pipe string, while preventing an occurrence of physical damage in the event that an improper command is issued that results in an application of excessive load.